Respecting GROUP BY Clause in a MySQL SUB-QUERY - mysql

Question

I have a query which returns some figures from a table of sales data. The table contains data for a number of different sales managers. I need to return data for the individual managers and also some calculated figures.
One of the figures I'm trying to get at involves a subquery. Getting the figures for each individual manager is fine and works well. The problem occurs when I am trying to get a figure which involves the use of a subquery. It seems that, though the outer query uses a group by clause to separate out individual salespeople, the subquery operates on the entire set.
Sample Data
name | Amount | Sell_at | Profit
--------------------------------
Fred | 1 | 3.99 | 0.99
Joe | 2 | 10.50 | 5.00
Fred | 5 | 20.00 | 15.00
Joe | 10 | 10.00 | 6.00
Desired result:
name | Total Profit | < 50% | > 50%
------------------------------------
Fred | 75.99 | 0.99 | 75.00
Joe | 71.00 | 60 | 10
SELECT
Account_Manager,
SUM(Profit * Amount) AS 'Total Profit'
(SELECT sum(Profit * Amount) from sales WHERE Profit * Amount / (Sell_at * Amount) < 0.5) AS '< 50%',
(SELECT sum(Profit * Amount) from sales WHERE Profit * Amount / (Sell_at * Amount) > 0.5) AS '> 50%'
FROM sales WHERE Invoice_Date = 'some date' GROUP BY Account_Manager
This gives me a row for each salesperson and their profit for that day, but the sub queries return figures totaled from the entire table. I could add a clause to the subquery WHERE in order to limit the result to the same date as the outer query, but ideally what I need to do really is to get the results for each individual salesperson.
Am I on the right track or is there another way I should be approaching this?

Answer 1

From your sample data and desired results it appears you only need a conditional aggregate:
select Name, sum(amount * profit) as TotalProfit,
Sum(case when Profit * Amount / (Sell_at * Amount) < 0.5 then Profit * Amount end) as '<50%',
Sum(case when Profit * Amount / (Sell_at * Amount) > 0.5 then Profit * Amount end) as '>50%'
from t
group by name

Answer 2

The expression:
Profit * Amount / (Sell_at * Amount)
is equivalent to just:
Profit / Sell_at
Use it in a CASE expression to perform conditional aggregation:
SELECT Account_Manager,
SUM(Amount * Profit) as TotalProfit,
SUM(CASE WHEN Profit / Sell_at < 0.5 THEN Profit * Amount END) `< 50%`,
SUM(CASE WHEN Profit / Sell_at > 0.5 THEN Profit * Amount END) `> 50%`
FROM Sales
WHERE Invoice_Date = 'some date'
GROUP BY Account_Manager;
You should also check for the case that Profit / Sell_at is equal to 0.5.
See the demo.

Answer 3

If you want to classify the rows based on their percentile, then use window functions. Let me assume that you want to know who is above and below average:
SELECT Account_Manager,
SUM(Profit * Amount) AS Total_Profit,
(CASE WHEN SUM(Profit * Amount) > AVG(SUM(Profit * Amount)) OVER ()
THEN 'Above average'
WHEN SUM(Profit * Amount) < AVG(SUM(Profit * Amount)) OVER ()
THEN 'Below average'
ELSE 'Average'
END) as relative_position
FROM sales
WHERE Invoice_Date = 'some date'
GROUP BY Account_Manager;